Signal Box Watcher provides replica Signal Box diagrams based on Warrington, Preston and Carlisle Power Signal Boxes for the West Coast Main Line, East Lancs & LYR main line, together with Merseyrail's Northern Line to Southport, Ormskirk and Kirkby. There is an index of locations.

These record the actual track circuit occupations in real-time, as provided by Network Rail's Open Source feed, so allowing the flow of trains through the various sections to be monitored.

The 'blocks' shown are marked by the signal number at the end of a block, and that train will have passed the actual signal location shown. For tracks signalled for bi-direction working, only those signals applying to the direction of travel will light up. Some locations feature trains that reverse 'in section' as happens on the new curve at Todmorden, which is used to reverse trains from Kirkby. So a train will arrive on the curve and the the signal behind it will light up showing the status change as a '5' for Empty Coaching Stock (ECS). But when entering the next block, the train describer changes to a '2' prefix, as it is now carrying fare-paying passengers.

For the time being, ground signals have also been included, where known. It is hoped these will allow a better understanding of how and when some of the lesser trackage is used. The home signal off the Deepdale branch at Preston is featured but don't expect a movement anytime soon. Some interesting anomalies have been observed, such as the Up Loop at Vitriol Works can be clearly seen on the 225 Studio video as having track and a lit signal, but no connections to the main line!

Some signals have provision for holding multiple trains as on certain platforms or on goods loops. They have a letter displayed before the signal number, such as A, B, C or X. The working of these can be clearly seen at Southport where two identities are shown: the inbound service by the stop block will have a letter 'S' in the train describer, and the outer Liverpool-bound service will show a 'U'. In reality, this is one and the same train with two identities, although the platforms can hold two separate 3-car sets. Some odd-ball headcodes also turn-up; at Southport in the Wallside siding for 24-hours was 'RIP.', and another at Platform 1 shown as '/RIP'. On that occasion it was possible to track the replacement '5X02' train being whistled up from Kirkdale and run ECS to Southport to replace the failed unit.

The actual diagrams are drawn form a number of sources. Much use has been made of the original BR, Railtrack and Network Rail re-signalling diagrams as issued to staff when the power boxes were commissioned. Google Earth has been used to check the current (c. 2009) layout and reference has also been made to the Railway Track Diagrams published by TRACKmaps. Should there be a difference of opinion, Google Earth has been favoured (the camera can't lie unless the tracks concerned are in shadow or badly overgrown). For lines for which re-signalling diagrams are not available, the excellent 225 Studio cab ride videos have been used to map track layouts and signal locations.Some sections of line do not feature in the NR TD feed, such as the line from Salwick to Blackpool or at Wigan Wallgate. However, these are expected to come on line as the sphere of the Manchester Signalling Centre is extended.The occupied block sections populate approximately 15 seconds after loading the page.The area current covered is shown on the map below.